Amniotic fluid from human fetuses at 14 to 16 weeks gestation where both parents are heterozygous for sickle cell anemia will be examined for evidence of homozygosity for sickle cell anemia. For this purpose heterokaryons of the fetal fibroblastic and/or epithelial cells in amniotic fluid with immature chick embryonic erythroblasts will be prepared and examined for their ability to synthesize human hemoglobin in general and hemoglobin S without simultaneous production of hemoglobin A in particular. Second, amniotic fluid itself will be examined for the presence of hemoglobin S without hemoglobin A, or of the corresponding globin peptide chains which might be present in small amounts. Column chromatography, electrophoretic techniques and immunological detection will be employed.